Julia Harvey: Pollock on Deck/The Beautiful, the Strange and the Interesting, August 3, 2013

NOAA Teacher at Sea
Julia Harvey
Aboard NOAA Ship Oscar Dyson (NOAA Ship Tracker)
July 22 – August 10, 2013    

Mission:  Walleye Pollock Survey
Geographical Area of Cruise:  Gulf of Alaska
Date:  August 3, 2013 

Weather Data from the Bridge (as of  00:00 Alaska Time):
Wind Speed:  26.5 knots
Temperature:  13.6 C
Humidity:  84%
Barometric Pressure:  1014.6 mb

Weather Update:
A low pressure system is in the north Pacific and we are having increase winds and swells.

Science and Technology Log:

We listened. We fished. Now what?

Before reporting to the fish lab, I must gear up.  Slime gear keeps the scales and goo off of my clothes.

slime gear
Preventing head to toe slime.
Julia Harvey
That is me holding coral while in my slime gear.

Fish are emptied out of the net and onto the table outside the fish lab.

fish table
The fish caught in the trawl net are emptied onto this table.

We can control how many fish land on the conveyor belt by raising the table and opening the door.

conveyor belt
As Darin opens the door, the fish will slide from the table to the conveyor belt.

The fish on the conveyor belt are separated by species.

Separating species
As the fish come off the table, Jodi and I separate the species while Darin weighs them.

In this blog we will focus on the pollock that were caught.

sorting pollock
Sorting pollock

Pollock are gathered into baskets and weighed.

Basket of pollock ready for the scale.

We group the pollock into 3 groups; age 1, age 2 and age 3+.  Each group as an entirety is weighed.  Each age group has a somewhat different protocol for processing.  Fifty specimens that are age 1 will be measured with the ichthystick and 10 will also be weighed.

To measure a pollock put his head at zero and use the magnetic reader to mark his fork length.

Fish that are age 2 are processed as age 1 but are also sexed.

When measuring a pollock on an icthystick, one measures from the head to the fork in the tail.  The icthystick (a magnetic board for measuring fish) is connected to a computer that automatically records the data.

The larger pollock are grouped by sex. To do this, we cut open their abdomen and look for ovaries or testes.

sexing fish
The abdomen must be opened to determine the sex of the pollock

Then all of the fish (or at least 300) are measured on the icthystick.  Forty will be measured and weighed and set aside for otolith removal.

otolith removal
Otoliths are removed.

Otoliths are made of calcium carbonate and are located directly behind the brain of bony fishes.

These are otoliths that were removed from an adult pollock.

They are involved in the detection of sound and the process of hearing.  The age of the fish can be established by counting the annuli much like one does when counting tree rings.

Scientists can count the rings of growth.

This age data allows scientists to estimate growth rates, maximum age, age at maturity, and trends of future generations. This data is vital for age based stock assessment models.  These fish are weighed and measured.  Otoliths are removed and placed in jars with glycerol thymol.

The jars have bar codes on the side so that the otoliths are linked to the fish’ weight, length and sex.

The otoliths are sent to Seattle for more detailed analysis of age. These results will be used to correspond length to age in the stock assessment report.

Sometimes, ovaries are removed and sent to other scientists for further histological study.

Other organisms that are caught alongside the pollock are counted and measured as well.  The catch might include Pacific ocean perch, salmon, herring, viper fish, lantern fish, jellyfish, squid, and capelin.  Below are a few of the normal finds and the rest can be found in my personal blog account “the beautiful, the odd and the interesting”.

Pacific ocean perch

Personal Log:

The beautiful, the odd and the interesting

This trip is not just about pollock.  When we bring any of the nets in there is the possibility of weirdness and other things that catch my eye.  Jodi is always filling me in on the uniqueness of our discoveries.  And Darin lets me save organisms for photographing later.

My favorite find so far is the lumpsucker.  As Jodi says, they have gentle brown eyes and they do.  They also have suckers on the bottom that allow it to stick to substrate.

Close up of lumpsucker

The Methot trawl went close to the bottom and picked up a handful of brittle stars.  At first, when they were mixed with all of the krill, it looked like a bunch of worms.

brittle stars
Brittle star collected from a methot trawl.
brittle stars
brittle stars

Pollock do eat young pollock.  We found evidence of this when Darin opened the stomach of an adult and discovered partially digested age 1 pollock.

pollock stomach
This pollock had feasted earlier on young pollock.

Lanternfish (Myctophids) make up a huge amount of the deep sea biomass.  They have photophores along their sides for producing light.

Lantern Fish

The adult Pacific sandfish bury themselves in the sand with only their mouths protuding.

Sand Fish

sand fish
This sand fish was not happy with me.

Prowfish lack pelvic fins.  They have continuous teeth to feed on jellyfish.


When I think of deep ocean fish I think of the viperfish with its needle sharp teeth.

viper fish
Viper fish with finger for scale.

This cute mud star came up with the brittle stars.  It was also referred to as the cookie cutter starfish because it resembles a shortbread cookie.

mud star
Mud star

Salmon are good swimmers and usually escape the net.  A few are caught at the surface.

sockeye salmon

When we were in Kodiak, I would watch the moon jellies drift by.  Now we are catching several different species of jellyfish like this sunrise jelly.

One of many species of jellyfish I have seen.

Jodi always has a keen eye for finding nearly invisible creatures.  The arrow worm is a voracious predator.  They immobilize their prey with neurotoxins.

marine worm
arrow worm

I had never heard of a sea mouse before this cruise.  Now I have.  Except it is not a rodent.  It is a carnivorous worm that feeds on hermit crabs and other worms.  It is also a scavenger like a vulture.

Actually a worm
Sea Mouse

Some isopods are parasitic and will feed off of the blood of fish in the gill chamber.  I prefer their cousins the pill bugs.

parasitic isopod
sea pens
sea pens
sea anemone
sea anemones

Did You Know?

When we are all measuring and weighing away in the lab, it sounds like a video game.  Each machine has it’s own unique sound effects.  This allows scientists to have confidence that their data was recorded.

Lab machines
Scanning the bar code.
machine noise
All machines have unique recording sounds


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